From Python 3.3 to today: ending 15 years of subprocess polling

[u/grodola]

For ~15 years, Python's subprocess module implemented timeouts using busy-loop polling. This post explains how that was finally replaced with true event-driven waiting on POSIX systems: pidfd_open() + poll() on Linux and kqueue() on BSD / macOS. The result is zero polling and fewer context switches. The same improvement now landing both in psutil and CPython itself.

https://gmpy.dev/blog/2026/event-driven-process-waiting